Synthesis and integration of a DNA copy of the viral RNA forms a part of the life cycle of avian sarcoma virus (ASV) necessary for both replication and cell transformation. I will use: restriction endonucleases, agarose gel electrophoresis, molecular hybridization, DNA sequencing and DNA transfection to characterize the synthesis and structure of the viral DNA (vDNA) made in vivo. The central goals of this project include: (1) determination of the role of host cell factors and viral enzymes in the synthesis of vDNA in vivo; (2) purification and DNA sequence analysis of the termini of the linear vDNA molecules to determine its relationship with the viral RNA and the mode of circularization; (3) definition of the regions of the viral genome present in the various circular vDNA molecules formed in ASV-infected cells; (4) delineation of the biological activity of the various forms of unintegrated vDNA; and (5) characterization of the integration site of the proviral DNA.